The present invention is a silicone rubber composition for use in electrical wire covering. Specifically the present invention is a silicone rubber composition for use in electrical wire covering which provides good electrical insulation and which makes it possible to prevent bonding or adhesion between electrical conductors and the silicone rubber (hereafter referred to as "core wire adhesion") in cases where the electrical conductors, such as copper wires or tin-plated copper wires, are covered by the silicone rubber.
Silicone rubbers are superior in terms of heat resistance, cold resistance, and weather resistance and are also superior in terms of electrical insulation. Accordingly, such rubbers are widely used as electrical wire covering materials. However, silicone rubbers of this type suffer from the drawback of low mechanical strength compared to commonly used organic rubbers. Accordingly, in the case of silicone-rubber-covered electrical wires it is necessary to reinforce the covering material by installing a braided material, such as a braided glass material, on top of the silicone rubber insulating layer. Furthermore, various types of varnishes are used to tie such braided materials together. As a result, when such varnishes are cured by means of heat treatment, core wire adhesion tends to occur between the silicone rubber insulating layer and the electrical conductor. A similar phenomenon also occurs in cases where the silicone-rubber-covered electrical wire is subjected to a secondary heat treatment in order to improve the electrical characteristics.
This core wire adhesion phenomenon is an extremely important problem from the standpoint of finishing. Specifically, in the case of terminal finishing such as soldering of silicone-rubber-covered electrical wires, core wire adhesion occurs so that some silicone rubber remains on the stripped portions of the electrical conductor, thus making it impossible to complete terminal finishing. Conventionally, a method in which a composition formed by adding a fatty acid or a metal salt of a fatty acid and powdered zinc oxide to a silicone rubber composition and curing by heating with 2,4 dichlorobenzoyl perozide has been used as a method for preventing such core wire adhesion (Japanese Patent Application Kokoku No. 62-26124). However, in this method, large quantities of the fatty acid or metal salt of a fatty acid must be added in order to prevent core wire adhesion. As a result the electrical characteristics, as typified by the electrical insulation ability, tend to drop so that the composition obtained is not always satisfactory as a silicone rubber composition for use in electrical wire covering.
Therefore, the object of the present invention is to provide a silicone rubber composition which has good electrical insulation characteristics and which also has a superior resistance to core wire adhesion.